import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        System.out.print("僵王血量：");
        Scanner scanner = new Scanner(System.in);
        int zombieHealth = scanner.nextInt();
        scanner.close();

        int hit = 0;
        int criticalHit = 0;

        while (zombieHealth > 0) {
            hit++;
            zombieHealth -= 2;
            criticalHit++;

            if (criticalHit == 3) {
                zombieHealth -= 10;
                criticalHit = 0;
            }
        }

        System.out.println(hit);
    }
}